A solid polymer-type fuel cell comprised of a cathode electrode, an anode electrode, and such a polymer electrolytic membrane as a membrane of an ion exchange resin having ion conductivity interposed therebetween starts generating electricity by, for example, supplying a fuel gas such as hydrogen gas to the anode electrode and an oxidant gas such as an oxygen gas or air to the cathode electrode thereby to cause an electrochemical reaction and convert the chemical energy of the fuel gas into electric energy (electricity).
Such solid polymer-type fuel cell is usually constituted of a fuel cell assembly composed of a plurality of stacked unit cells. Between adjacent single cells are provided separators. Each separator is provided with fuel gas passageways and oxygen gas passageways, with which the fuel gas and the oxidant gas are isolated. Each electrode and its adjoining separator need to be gas-sealed tightly thereby to prevent the leakage of fuel gas or oxidant gas from the edge or periphery of the polymer electrolytic membrane. Therefore, in assembling a fuel cell, a sealing structure is usually constructed by having a rubber packing (particularly, a thin rubber packing) made by compression molding, injection molding, or by punching out of a sheet be present between an electrodes and a separator.
In the sealing structure described above, however, the gas sealing against the fuel gas and the oxidant gas needs to be strictly retained for a long period of time, leading to a need for the rubber packing to be improved in its integrity and durability. Since the above-described rubber packing is a very thin membrane, forming such flexible packings by compression molding or injection molding not only results in variations in film thickness consequently leading to a lack in integrity but also makes their positioning at predetermined locations of the fuel cell difficult. Moreover, when assembling a fuel cell, the rubber packings are sometimes deformed or dislodged and therefore unable to provide a sure sealing.
U.S. Pat. No. 5,176,966 discloses the fabrication of fuel cells, in which a solid polymer ion exchange membrane and carbon fiber paper layers between which the membrane is interposed are heat-pressed for unitarily joining them into a single assembly, and the single assembly is processed to provide the assembly with sealing grooves. Then, a sealant of silicon rubber is injected into the grooves for sealing, and a fuel cell is assembled by using guide pin holes. The fabrication of this fuel cell, however, involves providing the carbon fiber paper layers integrally joined to the ion exchange membrane and constituting the unit assembly with sealing grooves. In addition to having the possibility of giving damage to the carbon fiber paper layers, this is not easy, much less the injection of the sealant into the grooves.
Japanese Patent Application Laid-Open No. 92450/1998 (JP-A-10-92450) discloses a sealing material for sealing a cell and separators constituting a solid electrolytic fuel cell, in which the sealing material is a glass material which softens at a temperature lower than the operating temperature of the solid electrolytic fuel cell and crystallizes at the operating temperature to be solid crystalline glass. Such sealing material, however, needs to be set at a predetermined place between the cell and the separators with accurate positioning. As a result, an easy and efficient assemblage of the fuel cell cannot be achieved.